High-frequency magnetron



June 16, 1953r c. v. LITTON 2,642,551

HIGH-FREQUENCY MAGNETRON Filed May 8, 1950 INVENTOR CHAR/.E6 Il L TTON ATTORNEY Patented June 16, 1953 UNITED STATES" PATENT OFFICE HIGH-FREQUENCY MAGNETRON Charles V. Litton, Redwood City, Calif. Application May 8, 1950, Serial N o. 160,749

'7 Claims. (Cl. 315-39) This invention relates to generators of ultrahigh frequency and particularly to magnetrons constructed to produce a large amount of power at the ultra high frequencies.

It is known in the prior art that the power available from a magnetron may be increased if a plurality of magnetrons are stacked together or if a single magnetron is increased in size. With an increase in size or in frequency of oscillations, undesired and extraneous modes occur more readily, which may be eliminated if one provides slots in the anode structure which dei-mes the cavity resonators of the magnetron. These slots are arranged at predetermined points spaced along the length of the anode structure in a direction parallel to the magnetron cathode which is coaxially mounted with respect to the cavity resonators. These slots prevent ultra high frequency waves from developing in the resonators in certain extraneous modes and particularly in those modes in which the electric field component is parallel to the axis of the magnetron. In particular they eliminate the longitudinal mode of operation of the magnetron by preventing current from flowing in an axial direction along the edges of the vanes or partitions which denne the cavity resonators of the magnetron. An example of such slots is given in the U. S. Patent No. 2,450,023 issued to Spencer.

In copending application Serial No. 122,634 filed October 21, 1949, on Simplitron Magnetron I have disclosed another method of preventing extraneous modes from developing in magnetrons adapted for high power operation. In said application it is shown that where a plurality of magnetrons are stacked together, electromagnetio wave coupling between resonators of the several magnetrons will tend to pull the magnetrons into oscillation in a single mode and hence at a single frequency.

It is an object of this invention to provide an improved magnetron for more stable operation at high frequency with greater power output than was heretofore possible.

It is a further object of this invention to provide both slots and an electromagnetic wave coupling means between the cavity resonators of a magnetron in such a manner that the magnetron may be constructed of a greater size than heretofore possible and hence it may provide greater power output.

In particular I carry out the above-mentioned objects by providing a slot a quarter wave length long at the operating frequency in each vane or partition which defines the cavity resonators of the magnetron and I further provide an electromagnetic wave coupling path between at least a pair of adjacent resonators in the magnetron for locking the resonators into operation in the desired mode.

The method of connection serves deliberately to reenforce a push-pull mode, which naturally wants to come in as'the anode is made axially longer. Thus the sections individually operate with constant elds but theslots permit a phase reversal at appropriateY points along the anode. AS this is the natural tendency, the slots and feedback loop re-enforce the tendency and a very stable long-anode configuration results. The system will couple eic'iently to the electron lstream. It is noted that the cathode may need a ring mounted on it in the plane of the slots to maintain high electronic eiiiciency and low back bombardment.

The above-mentioned objectsand features and further objects and features will be better understood by reference to the following description and the copending drawings of which:

Figure l is a diagrammatic perspective view of a pair of adjacent resonators of a magnetron incorporating an embodiment of my invention;

Figure 2 is a longitudinal sectional view of'a magnetron incorporating features of my invention;

Figures 3 and 4 are cross sectional and side views of the magnetron of Figure 2; and

Figure 5 is a diagrammatic perspective view of a pair of adjacent cavity resonators of a magnetron illustrating a further embodiment of my invention. v

The theory of the operation of my invention is best understood by reference to Figure l in which three vanes l, 2 and 3 are shown, said vanes comprising three vanes of a magnetron in which'a plurality of vanes arranged radially about a central cathode form the cavity resonators. The normaloperation of the magnetron is in the transverse mode. In this mode adjacent ends of these vanes are out of phase at the ultrahigh frequency, as is shown by the -land signs. To prevent extraneous modes from developing and particularly to prevent ultra-high frequency current from flowing in an axial direction along the edge of the vanes, slots 4, 5 and 6 are provided therein. Spencer in the above cited patent has shown these slots as capacitive loads for the longitudinal mode of operation. They increase the frequency of the longitudinal mode 4and when the longitudinal mode frequency is tials thereon which are 180 out of phase. In

order to ensure that the magnetron does operate in this manner, I propose to provide further mode stabilizing means in the form of a coupling between the upper half of one cavity resonator and the lower half of an adjacent cavity resonator. As will appear from the discussion above and from the -I- and signs shown in Fig. 1 which represent the ultra-high frequency potentials at the edges of the vanes at a given instance of time, the coupled portions of the two cavity resonators will be oscillating in phase.

If the coupling path 'I is made an integral multiple of a half wave length long at the operating frequency and if it is coupled into each of the cavity resonators as discussed in my copending application mentioned above with or without phase reversal depending on whether the length is an odd or even multiple of a quarter Wave length, the coupling path will tend to lock the coupled portions of the adjacent cavity resonators into in-phase operation. As illustrated in Figure 1, in the upper half of the cavity resonator formed by vanes I and 2 and the end wall 8 coupling them, ultra-high frequency current will be flowing in the end wall from vane 2 to vane I at a given instance of time. At the same instance of time ultra-high frequency current will be flowing in end wall 8 between vane 2 and vane 3 in the direction from the vane 2 to vane 3. That is, oscillations in the adjacent cavity resonators formed by vanes I, 2 and 3 are out of phase. In the lower portions of these two cavity resonators as la result of the quarter wave length slots at the midpoints of the vanes, the oscillations will be out of phase and ultra-high frequency current will be flowing in the end wall 8 as a result'of the ultra-high frequency oscillations in the cavity resonator between vanes 2 and 3 in the direction from vane 3 to vane 2. If the electromagnetic wave path 'I is an integral multiple of a half wave length long at the operating frequency and coupled into the resonators as discussed above, no current will ow through it and hence no energy will be transferred from the upper part of the resonator between vanes I and 3 to the lower part of the resonator between vanesl 2 and 3 when they are operating in the same mode. If they tend to oscillate in different modes coupling path 'I will cause ultra-high frequency energy to be transferred between the two cavity resonators so that they are pulled back into oscillation in the desired mode.

Thus both the slot and the electromagnetic wave coupling path between resonators are used to stabilize the mode of operation of the magnetron. Figures 2 through 4 show in detail the structure of a magnetron embodying the quarter wave length slot and the electromagnetic coupling means between resonators of the magnetron.

mounted coaxially inside of eight vanes I0. The vanes I0 are arranged radially about the cathode 9 and form cavity resonators with the cylindrical end wall II. The vanes are provided with strap pairs I2 and I3 one in the upper and the other in the lower portion of each vane. The straps, as is well known in the art, are connected to alternate vanes and tend to cause the resonators between the vanes to oscillate in that mode in which thel-ultrahighfrequency potential, at the inner end of each vane is 180 i out of phase with that at an adjacent vane.

In Figures 2 and 3 aA cathode 9 is shown 75 Each Vane I 0 has a slot I4 at the midpoint of the vane-along the axis of the resonator and extending radially from the cathode. A wave path is shown in the form of a wave guide I5 coupled between a pair of adjacent cavity resonators I6 and I'I by means of resonator to wave guide matching sections I8 and I9. The wave guide is provided with telescoping portions v20 so that ,it may be adjusted to the desired length. As shown in Figure 4 it is coupled 'between the upper portion of resonator I6 and the lower portion Vof resonator I1. A ring 2| is provided about cathode 9 in the plane of slots I4 to protect it against back bombardment in this area.

It is not intended that my invention be limited to the particular form of cavity resonator, to the particular shape of the slot or to the particular type of wave guide coupling means. In the first place it is obvious that more than one slot may be provided. In Figure 5 there is shown three vanes 22, 23 and 24 of a magnetron formed by a plurality of vanes arranged radially about a cathode. The vanes form a pair of adjacent cavity resonators 25 and 26 with end wall 21. Each vane is provided with three slots 28, 29 and 30 extending a quarter of a wave length into the vane from the inner edge which will be adjacent the cathode. In a manner similar to the function of the slots as discussed in connection with Figure 1, these slots will cause the portions of the cavity resonators on one side to oscillate out of phase with the portions of the cavity resonators on the other side. This is illustrated by the -I- and signs shown on the inner edges of the several vanes between the slots and illustrating the value of the high frequency voltage that will appear at the edges of said vanes at a given instance of time. A pair of coupling means 3I and 32, similar to coupling lmeans 'I illustrated in Figure 1, are provided for the magnetron with the three slots in each vane. Coupling path 3| is arranged between the upper portion of resonator 25 and the portion. of resonator 26 which is between vanes 28 and 29. Coupling path 32 is arranged between the portion of a resonator 25 which is between slots 29 and 30l and the lower portion of resonator 2B. 'Ihe coupled portions of the resonators will be oscillating in phase as discussed in connection with Figure 1 and if the paths 3`I and 32 are coupled to the resonators `without phase reversal they should be made an even multiple of a half wave length long at the operating frequency in order that they will lock the coupled portions of the resonators into in-phase operations as is desired.

I have described my invention with reference to two preferred embodiments. ItV isnot intended that the invention'should be limited to these particular embodiments, but only as dened in the claims which follow.

What I claim is:

1. A magnetron for stable operation at ultrahigh frequencies with high power output comprising a cathode, an anode structure about said cathode having walls defining a plurality of cavity resonators, each of said walls being provided with a resonant slot extending radially from said cathode, and an electromagnetic wave path device coupled from a region in one of said resonators spaced axially from one of said slots in one direction to a region in another of said resonators spaced `axially from said one slot in the opposite direction.

2. A magnetron for stable operation of ultrahigh frequencies with high power output comprising a cathode and an anode structure a'bout said cathode having Walls defining a plurality of cavity resonators, each of said walls being provided with a slot substantially at the midpoint and extending lengthwiseradially from the edge of said wall adjacent said cathode, said slot being substantially a quarter Wave length long at the frequency of vibrations in the longitudinal mode in said cavity resonators.

3. A magnetron for stable operation at ultrahigh frequencies with high power output comprising a cathode, an anode structure about said cathode having vanes dening a plurality of cavity resonators, each of said vanes being provided substantially at its midpoint with a slot extending radially from said cathode, said slot being substantially a quarter wave length long at the frequency of vibrations in the longitudinal mode in said cavity resonators, and an electromagnetic wave path device coupled from a region in one oi said resonators spaced axially from one of said slots in one direction to a region in another of said resonators spaced axially from .said one slot in the opposite direction, said path device having a length to lock said coupled regions into in-phase oscillations.

4. A magnetron according to claim 3 in which co-phasal coupling means are positioned between said path device and said resonators and said path device is substantially an even multiple of a half wave length longrr at the frequency of vibrations in the transverse mode in said cavity resonators.

5. A magnetron according to claim 3 in which coupling means are positioned between said path device and said resonators, one of said coupling means providing phase reversal for the electromagnetic waves, said electromagnetic wave path device being substantially an odd multiple of a half wave length long at the frequency of vibrations in the transverse mode.

6. A magnetron for stable operation at ultrahigh frequencies with high power output comprising an elongated cathode, an anode structure about said cathode having vanes defining a plurality of cavity resonators, each of said vanes being provided with a plurality of resonant slots evenly spaced axially along said vanes, and an electromagnetic wave path device coupled from a region in one of said resonators spaced axially from one of said slots to a region in another of said resonators spaced axially from said one slot in the opposite direction, andan additional electromagnetic wave path device coupled from a region in one of said resonators spaced axially from said one slot and from either of said rsttwo-mentioned regions to a region in another of said resonators spaced axially from said one slot and from any of said first-three-mentioned regions, said wave path devices each having a length to lock said coupled regions into in-phase oscillations.

'7. In a magnetron including a cathode and an anode about said cathode having wallsfdening a plurality of cavity resonators, means for stabilizing the operation of said magnetron at ultra-high frequencies with high power output comprising means in each of said walls dening a resonant slot extending radially from said cathode, rand means coupling a first region in one of said resonators spaced axially from one of said slots in one direction to a second region in another of said resonators separated from said one resonator by an even number of resonators, said second region being spaced axially from said one slot in the opposite direction from said first region, said means being designed to lock said regions into inphase oscillations.

CHARLES V. LITTON.

References Cited in the file 0f this patent UNITED STATES PATENTS 

